Impact tools



1961 H. HARRISON ETAL IMPACT TOOLS 2 Sheets-Sheet 1 Filed Jan. 25, 1954 .HARRISON mqz "235* THEIR ATTORNEY Oct. 31, 1961 H. HARRISON ET AL IMPACT TOOLS 2 Sheets-Sheet 2 Filed Jan. 25, 1954 '1 iii I! 9 N 8 O 0 mm 7 7 m 2 NRR 8 ERA 9 MM 7 l C Mn Y 5 RRY 7 NNB 2 w EE 7 87 HH 7 H 3 3 v 1 y n\ W T M w 1 a, H A I. r \r k Z; l w

THEI R ATTORNEY United States Patent Office 3,006,446 Patented Oct. 31, 1961 3,006,446 IMPACT TOOLS Henry Harrison and Henry C. Harrison, Port Washington, N.Y., assignors to Ingersoll-Rand Company, New York, N.Y., a corporation of New Jersey Filed Jan. 25, 1954, Ser. No. 405,708 1 Claim. (Cl. 192-305) This invention relates to impact tools and more par ticularly to a torque limiting device for impact tools of the type adapted to deliver a series of rotational hammer blows in rapid succession to an anvil for rotating a work-piece.

In the field of rotary impact tools there has long been a need for a device for indicating or limiting the amount of torque, or twisting force, applied by the tool to work such as screws, nuts and the like. This need arises from the fact that in absence of such a device the degree of tightness-short of maximum torque of the tool-is dependent on the guess of the operator. In most circumstances it is desirable to avoid such guess work, even by an experienced operator, and in some circumstances the degree of tightness of the work must be maintained within narrow limits. In the latter instance the operator, after using an impact tool to tighten the work to what is believed the proper degree, is generally required to disengage the tool from the work and then check the tightness of the work by the use of a separate tool, such as a torque wrench.

The present invention eliminates such guess work and the need for additional tools by the provision of a torque limiting device incorporated in the impact tool. More particularly, the impact tool is provided with a spring connected between the anvil and the work-piece for transferring rotary motion thereto. The spring is prestressed in such a way that it serves below a predetermined degree of tightness of the work as a relatively rigid connection between the work and the tool, and as a relatively elastic connection above said degree of tightness. Thus the prestressed spring serves as a means to transmit substantially all of the energy of the hammer or anvil to rotate the work until the work reaches some desired degree of tightness; thereafter part of the energy of the hammer is accumulated by the spring. The energy thus accumulated by the spring may be expended in actuating a shutdown device for halting the operation of the impact tool at a predetermined degree of tightness of the work.

It is accordingly one object of this invention to provide a force transmitting element for impact tools which is adapted to serve as a relatively rigid connection below a predetermined force transmitted thereby and as a relatively elastic connection above said predetermined force.

Another object of this invention is to provide a torque limiting device for rotary impact tools which is operative above some predetermined turning force of the tool to accumulate at least part of the energy of such turning force to limit the turning force applied by the impact tool to the work.

Another object of this invention is to utilize such accumulated energy to actuate a shutdown mechanism for the impact tool.

Another object of this invention is to provide a prestressed spring connection for transferring the turning force of the anvil to a work-piece and to shut oif the impact tool whenever the spring is further stressed by the anvil.

A further object of this invention is to make the torque limiting device adjustable so that the maximum turning force transferred from the anvil to the work-piece may be varied over a relatively wide range.

Further objects of this invention will become obvious from the following specification and drawings in which FIGURE 1 is a vertical elevation, partly in section, of a rotary impact tool provided with a preferred form of the torque limiting device,

FIG. 2 is a vertical elevation showing an alternate form of the spring,

FIG. 3 is a transverse view taken through FIG. 1 along the line 33 looking in the direction of the arrows,

FIG. 4 is a transverse view taken through FIG. 1 along the line 44 looking in the direction of the arrows,

FIG. 5 is a transverse View taken through FIG. 1 along the line 55 looking in the direction of the arrows and showing the adjusting mechanism for varying the maximum torque applied to the work,

FIG. 6 is a transverse view taken through FIG. 2 along the line 6-6 looking in the direction of the arrows,

FIG. 7 is a vertical elevation, partly in section, of the rear end portion of the impact tool of FIG. 1 and shows details of the manual motor control (switch ofi position) and tripping mechanism for automatically shutting down the motor,

FIG. 8 is a sectional elevation showing the mechanisms disclosed in FIG. 7 with the motor switch in the on position,

FIG. 9 is a sectional elevation showing the mechanisms disclosed in FIG. 7 showing the tripping mechanism in its tripped position,

FIG. 10 is a perspective view, partly in section, showing the connection between the spring means and anvil,

FIG. 11 is a development of the jaws shown in FIG. 10,

FIG. 12 is a cross sectional view taken through FIG. 7 along the line 1212 and looking in the direction of the arrows and shows a detail of the tripping mechanism, and

FIG. 13 is a transverse view taken through FIG. 7 along the line 13-13 looking in the direction of the arrows.

Referring to the drawings an impact tool capable of delivering a series of rotary blows in rapid succession for tightening screws, nuts and similar Work is shown provided with a preferred form of the torque limiting device. The tool comprises, in general, a casing 10 housing a motor 12 connected through suitable gearing 14 to rotate a hammer element 16. Positioned in the forward end of the casing 10 and coaxial with the harnmer element 16 is an anvil element 19 having a pair of dogs, or jaws, 20 arranged to engage a similar pair of dogs 22 on the hammer 16. The anvil element 19 is connected through the torque limiting device 24 to a workpiece 26 for transmitting the twisting force of the hammer to the work.

In the tool shown by way of illustration only, the motor 12 rotates continuously during the entire tightening operation. The hammer 16, on the other hand, rotates continuously only during the initial, or rundown, portion of the tightening cycle, when the work is relatively loose. During this period the hammer 16 remains engaged to the anvil element 19. As the work is progressively tightened the resistance to rotation of the anvil is proportionally increased and when this resistance exceeds some predetermined torque, or twisting force, the hammer 16 is cammed out of engagement with the anvil element 19 and then quickly accelerated to strike a blow on the anvil element 19 to tighten the work.

In furtherance to this end the driving connection be tween the motor driven spindle '28 and the hammer 16 is in the form of a cam 30 comprising inverted V-shaped races 32 for balls 34 which engage the forward surface of an introverted shoulder 36 on the hammer 16. The hammer 16 is continuously urged into its forward posi tron (as shown in FIG. 1) into engagement with the anvil element 19 by means of a spring 38. When, however, the resistance to rotation of the anvil reaches some predetermined value, depending on the degree of tightness of the work, the anvil element 19 will slow down the speed of rotation of the hammer 16 to a value below that of the speed of rotation of the spindle 28. The rotation of the spindle 28 relative to the hammer 16 earns the balls 34 rearwardly moving the hammer 16 to compress the spring 38 and disengage the hammer jaws 22 from the anvil jaws 26. Upon disengagement of these jaws, the hammer is accelerated rotationally at the speed of the spindle 23 plus the rotational speed imparted to the hammer relative to the spindle 28 by the spring 38 in forcing the hammer forwardly along the cam 30 to move the hammer in position to strike a high velocity blow on the anvil 18.

It is to be noted that the magnitude of the turning force exerted by the hammer on the anvil, except for the force required to accelerate the anvil and associated parts 24, 54 and 57, is determined primarily by the resistance to rotation of the anvil by the work. For example, if a twisting force of only foot pounds is required to rotate a nut, then the hammer and anvil can exert only a 10 pound feet twisting force; similarly, only a 20 pound feet force is exerted when 20 foot pounds is required to rotate the nut. In practice, the twisting force required to rotate the nut will, of course, ordinarily vary throughout each blow of the hammer e.g., only 10 foot pounds may be required to rotate the nut at the start of the blow, and this torque will increase as the nut is tightened so that at the end of the blow to foot pounds torque may be required to rotate the nut. The energy in the hammer is roughly the same for each blow and accordingly, assuming identical tightening conditions and a relatively rigid connection between the hammer and the nut, the nut is rotated a greater amount by a blow when the work is loose than when it is tight.

The present invention is concerned with limiting to a predetermined amount the torque applied by the tool to the work. In furtherance to this end either the hammer element 16 or anvil element 19 is formed in two parts and one of the parts include a prestressed spring for transmitting rotary movement of one part to the other. For the purpose of illustration the anvil element only is shown in two parts, one part being designated as the anvil 18 and the other as the connection 57 between the anvil 18 and the workpiece 26. The latter connection 57 includes the prestressed spring 40.

More particularly, the spring 46 is connected at one end (at 50 FIG. 1) to the anvil 18, and a connecting element 39 serves as a means for engaging the other end of the spring to the work and to the anvil (at 59, 60 FIG. 4) in a prestressed condition. The engagement of the element 39 with the anvil is such as to permit relative movement in one direction between the anvil and the work.

With this arrangement the spring 49 serves as a relatively rigid member for transmitting substantially all the energy of the hammer to the work 26 so long as the twisting force of the spring 40 is below the pre-stressed torque of the spring. When, however, the work reaches a predetermined degree of tightness at which the twisting force of the anvil exceeds said prestressed torque, the spring 40 serves as an elastic connection and is further stressed permitting the anvil 18 to rotate relative to the work 26. Thus part only of the energy of the hammer blow is transferred to the work, part of the energy being expended in Winding the spring 40.

Referring in greater detail to the construction of the torque limiting device 24, the spring 40 shown in FIG. 1 includes a pair of concentrically positioned inner and outer tubes 42 and 44, respectively, secured together at their rearward end portions as by soldering. One end of the spring 40, the forward end of the inner tube 42, is engaged to the anvil 18 by means of a rod 48. The rod 48 is connected at its forward end 46 to the tube 42 and extends through the tube 42 for connection with the anvil by means of a square 50 engaged in a square hole 52 in the anvil 18.

The other end of the spring i.e., the forward end of tube 44, is connected to the Work 26. In furtherance to this end, mounted on the spring 40 and the anvil 18 is the means for engaging the spring to the work and engaging the spring 40 to the anvil in a prestressed position. In the form of the invention illustrated such means is shown as including the tubular shaped connecting element 39 connected to the forward end of the outer spring tube 44 by a pin 62 fitted in a hole 61 in a spring terminating cap 56 and fitted in a hole 61 in the cap 56. Three jaws 59 formed on the rearward end portion of the element 39 are adapted to engage a similar trio of jaws 60 on the forward end of the anvil 18 (see FIG. 10). A conventional socket 54 connects the element 39 to the work.

Referring to FIG. 2 a spring 96 having a cruciform cross section is shown as an alternate to the tubular spring 40. In order that the spring 96 may be used in the form of the invention shown in FIG. 1 it is provided with a square 97 at one end to engage the anvil and a transverse passage 98 at its opposite end to receive the pin 62.

In order to permit ready adjustment of amount of prestressing of the spring, the bore 58 is made larger than the pin 62 and a screw 66 is threaded in the connecting element 39 to bear against an end portion of the arm, or pin, 62 engaged to the spring 40. Threading of the screw 66 into the connecting element 39 results in rotation of the pin 62, and thus one end of the spring 40, in the counter clock-wise direction as viewed in FIG. 5. inasmuch as the opposite end of the spring 40 is held against rotation by the anvil 18, such rotation of the pin 62 results in winding, or Prestressing of the spring 46.

Prestressing of the spring 40 tends to rotate the connecting element 39 in the direction of rotation of the anvil during the tightening operation of the tool (right-hand rotation as viewed in FIG. 1) thereby urging the leading surfaces 63 of the jaws 59 into engagement with the trailing edges 64 of the anvil jaws 60. The length of the jaws 59 and 60 are such that when the element and the anvil 18 are placed in their assembled position with the spring 46, the jaws 59 and 60 are short of complete meshing (see FIGS. 10 and 11). This leaves a space between the leading surfaces 67 and the trailing edge 68 of the jaws 60 and 59, respectively, so that the anvil may be rotated relative to the connecting element 39 in the direction of rotation of the anvil' during the tightening operation to further tension the spring 40.

It is to be noted that, neglecting the inertia of the connecting element 39 and of the Work, the anvil cannot rotate relative to the connecting element 39 until the twisting force required to rotate the work exceeds the prestressed force in the spring. Thus, at the time the anvil exerts a twisting force in excess of the oppositely directed prestressed force of the spring, the Work has attained a predetermined degree of tightness corresponding to the prestressed force of the spring. Accordingly, by the use of a device responsive to the opening of the jaws 59 or 60 or operated by the accumulated energy of the spring 40 to halt the operation of the tool at this time, the torque applied by the tool may be limited to a known value. In the embodiment of the invention here described the energy accumulated by the spring in being further stressed is expended in augmenting the longitudinal disengaging movement of the hammer to operate a shut-down device.

The tripping mechanism shown by way of illustration is best seen in FIGS. 7, 8 and 9. The numeral 69 indicates a conventional slide-action trigger mounted in the tool handle 70 for actuating the motor control switch 89. The trigger 69 is constantly urged toward its forward, or shutdown, position by means of a spring 71 positioned in a cavity 72 in the trigger 69 and bearing on a pin 73 extending through longitudinal slots 75 in the trigger. Positioned within a slot 74 in the trigger is a two element link 76 pivotally connected at one end to the trigger 69 by means of a pin 77 and at its other end by pin 86 to a crank 78. The two elements 79 and 80 of the link 76 are pivotally connected together at their adjoining ends by a pin 82, and a spring 83' encircling the pin 77 bears against the element 79 urging it in a counter clock-wise direction (FIG. 8). Movement of the element 79 in such direction is limited by means of a pin 84 located to position the pin 82 slightly to the left (see FIG. 7) of a line between the centers of the pins 77 and 86. Thus the two elements 79 and 80 are normally held in a position by the spring 83 such that they serve as a relatively rigid single link to transmit rearward movement of the trigger 69 to rotate the crank 78 and actuate a pin 87 for closing the electric switch 89 to start the motor 12 (see FIG. 8).

In furtherance to the end that the longitudinal movement of the hammer 16 serves to shut 013? the motor 12, an L-shaped member 88 is slidably mounted in the casing with the foot of the L extending into the casing in the path of the longitudinal movement of the hammer. The foot is located at a point such that it will not be struck by the hammer during normal disengaging movement of the hammer, but will be struck whenever this movement is materially augmented by the spring 40.

The opposite end of the member 88 bears against one arm 90 of a bell-crank 91, the other arm 93 of the crank 91 bears on the link 76 at its joint or point of connection between the elements 79 and 80. A spring pressed plunger 92 acting against the arm 90 constantly urges the bell-crank arm 93 away from the link 76 and the member 88 toward its forward limiting position against a shoulder 94 on the casing 10.

When the disengaging movement of the hammer from the anvil is augmented by the spring 40 to such an extent that the hammer moves a sutficient distance longitudinally rearward to strike the member 88, rearward movement of the member 88 rotates the bell-crank 91 to break the link 76 and release the motor switch 89. That is, the arm 93 forces the element 79 in the clockwise direction until the center point of the pin 82 moves to the right and off center of a line between the opposite ends of the link 76 thereby breaking the link 76 and permitting the spring 95 in the switch 89 to rotate the crank 78 in a counter clock-wise direction to open the switch 89 and shut off the motor (see Fig. 9). When the trigger 69 is released, the spring 71 will move the trigger into its forward limiting position thereby moving the pin 77 away from the pin 86 to permit the spring 83 to rotate the element 79 into engagement with the pin 84 and reposition the trigger elements preparatory to actuating the switch 89 in the next tightening operation (see FIG. 7). The spring pressed plunger 92, immediately after the element 88 is struck by the hammer 16 will reposition the element 88 and rotate the bell-crank 91 out of the path of movement of the pin 82 to permit such resetting of the trigger mechanism.

Reviewing the operation of the torque limiting device it will be assumed that the impact tool has passed through the rundown period and has reached the hammering portion of the tightening cycle, i.e., the hammer 16 is periodically engaging and disengaging with the anvil 18 to deliver a series of hammer blows in rapid succession. So long as the degree of tightness of the work is below a predetermined value the torque developed by each hammer blow will remain below the prestressed torque in the spring 40 and the jaws 59 and 60 will, neglecting minor vibrations, remain in engagement (see FIG. 10). During this portion of the tightening cycle, the spring 40 serves as a rigid member for transmitting substantially all the torque developed by the hammer to the workpiece 26. When, however, the turning force of the anvil exceeds the prestressed turning force of the spring 40, the anvil 18 will rotate relative to the work 26, and hence the connecting element 39. This relative rotation moves the jaws 60 out of contact with the jaws 59 and winding or further stressing the spring 40. When, during this hammer blow, the turning force exerted by the hammer through the anvil on the spring falls below the spring torque, the spring 40 will unwind imparting a counter clock-wise movement to the hammer 16 to accentuate the disengaging movement between the hammer 16 and anvil 18.

More particularly, neglecting any rebound of the hammer, the magnitude of the normal disengaging movement of the hammer from the anvil after the hammer has moved longitudinally free of the anvil is dependent primarily on the difierence in rotational speed of the spindle 28 and the hammer 16 resulting from the inertia of the hammer. Thus, when the spring 40 imparts a counter clock-wise movement or artificial rebound to the hammer 16, this relative speed is increased by an equiva lent amount thereby causing the hammer to move longitudinally along the cam 30 a greater ditsance than when the spring 40 does not actuate the hammer 16. This increase in disengaging movement between the hammer 16 and the anvil 18, causes the hammer to strike the member 88 and actuate the shutdown device to shut ofi the tool.

Although a shutdown device is shown as being a desir able part of the torque limiter, it is to be understood that under circumstances where similar tightening conditions of a workpiece are repeated, as in assembly line operations, it is possible to use the torque limiter without the shutdown device. That is, by the proper choice of spring for a given impact tool, the tightness of the work is limited to the approximate desired amount in that when this point in the tightening cycle is attained the hammer energy is expended primarily in stressing the spring.

While we have shown and described specific forms of our invention, it is to be understood that various changes and modifications may be made without departing from the spirit of the invention as set forth in the appended claim.

We claim:

In a rotary impact tool having a casing, an anvil in the casing, a rotational hammer adapted to deliver a series of hammer blows to the anvil, said anvil having an elongated forwardly extending portion, a rotationally stressed spring element extending into said portion and engaged at its rearward end to said anvil against rotation relative thereto and adapted at its forward end portion to be engaged to a work piece, and means for connecting the spring element to the anvil to hold said spring in such stress position, said means including a connector engaged to the forward end portion of the spring against movement in either direction relative to the spring and having a loose interlocking connection with the anvil to permit limited relative rotation between the anvil and the forward end of the spring whenever the spring is additionally stressed by rotation of the anvil relative to the work piece.

References Cited in the file of this patent UNITED STATES PATENTS 2,049,273 Pott July 28, 1936 2,111,280 Connell Mar. 15, 1938 2,184,394 Moret-ti Dec. 26, 1939 2,238,380 Almen Apr. 15, 1941 2,254,261 Best Sept. 2, 1941 2,543,979 Maurer Mar. 6, 1951 2,576,851 Newman Nov. 27, 1951 2,608,118 Disser Aug. 26, 1952 2,717,672 Maurer Sept. 13, 1955 

